1. Field of the Invention
This invention relates generally to storage networks and, more specifically, to a network device on a storage network that segregates files into separately stored directory metadata and associated data such that a file server containing the directory metadata can appear to store data beyond its storage capacity.
2. Description of the Related Art
In a computer network, NAS (Network Attached Storage) file servers connected directly to the network provide an inexpensive and easily configurable solution for a storage network. These NAS file servers are self-sufficient because they contain file systems that allow interoperability with clients running any operating system and communication using open protocols. For example, a Unix-based client can use the NFS (Network File System) protocol by Sun Microsystems, Inc. of Santa Clara, Calif. and a Windows-based client can use CIFS (Common Internet File System) by Microsoft Corp. of Redmond, Wash. to access the same files on a NAS file server. Thus, NAS file servers provide true universal file access.
By contrast, more expensive and powerful SAN (Storage Area Network) file servers use resources connected by Fibre Channel on a back-end, or a dedicated network. A SAN file system is part of the operating system or an application running on the client. By heterogeneous client operating systems may require additional copies of each file to be stored on the storage network to ensure compatibility on the SAN file server. Additionally, communication between clients and file servers on a SAN use proprietary protocols and thus are typically provided by a common vendor. As a result, NAS file servers are preferred when price and ease of use are major considerations. However, the benefits of NAS storage networks over SAN storage networks also have drawbacks.
One drawback with NAS file servers is that there is no centralized control. Accordingly, each client must maintain communication channels between each of the NFS file servers separately. When NAS file servers are either added or removed from the storage network, each client must mount or unmount directories for the associated storage resources as appropriate. This is particularly inefficient when there are changes in hardware, but not in the particular files available on the network, such as when a failing NAS file server is swapped out for an identically configured back-up NAS file server.
A related drawback of decentralized control is that services must be separately purchased and installed to each NFS file server. Likewise, updates and maintenance of the services are separately provided. Furthermore, each installed service consumes data capacity that could be better used to server the main purpose of a storage network, which is to store data.
Therefore, what is needed is a robust network device to provide transparency for clients of decentralized file servers such as NAS file servers. Furthermore, the network device should provide a centralized directory service using a network file server that is uninhibited from data storage responsibilities and thus can store a directory hierarchy referring to an amount of data beyond a storage capacity of the network file server. Moreover, the directory service should enable additional centralized services that rely on directory information.